Pages: 16 (3841 mots) Publié le: 16 avril 2011
Chapter 6 Metabolism
The chemistry of life is organized into metabolic pathways
Metabolism = Totality of an organism’s chemical processes.
Property emerging from specific molecular interactions within the cell.
Concerned with managing cellular resources: material and energy.
Metabolism begins by the assimilation of nutrients into the body of an organism.
This results in a series ofstepwise chemical transformations of the nutrient structure.
There are two main pathways involved:
Catabolic pathways = Metabolic pathways which release energy by breaking down complex molecules to simpler compounds. (e.g. Cellular respiration which degrades glucose to carbon dioxide and water; provides energy for cellular work.). This applies to a pathway which proceeds to break down large complexstructures into simple molecules such as carbon dioxide, amino acids, ammonia and urea. Under this condition, the function is extraction (production) of energy from the bonds of the nutrients.
Anabolic pathways = Metabolic pathways which consume energy to build complicated molecules from simpler ones (e.g. Photosynthesis which synthesizes glucose from CO2 and H2O). So, this is a biosyntheticpathway leading to the production of large complex molecules such as polymeric molecules called polysaccharides, proteins or nucleic acids. This pathway consumes energy. Anabolic steroids promote biosynthetic pathways, particularly the biosynthesis of proteins in muscles.
Metabolic reactions may be coupled, so that energy released from a catabolic reaction can be used to drive an anabolic one.[pic]
and there are several ways in which the two pathways are linked.
Organisms transform energy
Energy = Capacity to do work
Kinetic energy = Energy in the process of doing work (energy of motion). For example: Heat (thermal energy) is kinetic energy expressed in random movement of molecules. Light energy from the sun is kinetic energy which powers photosynthesis.
Potential energy =Energy that matter possesses because of its location or arrangement (energy of position). For example: In the earth’s gravitational field, an object on a hill or water behind a dam have potential energy. Chemical energy is potential energy stored in molecules because of he arrangement of nuclei and electrons in its atoms.
Energy can be transformed from one form to another. For example:
Kineticenergy of sunlight can be transformed into the potential energy of chemical bonds during photosynthesis.
Potential energy in the chemical bonds of gasoline can be transformed into kinetic mechanical energy which pushes the pistons of an engine.
The energy transformation of life are subject to two laws of thermodynamics
Thermodynamics = Study of energy transformations.
First Law ofThermodynamics = Energy can be transferred and transformed, but it cannot be created or destroyed (energy of the universe is constant).
Second Law of Thermodynamics = Every energy transfer or transformation makes the universe more disordered (every process increases the entropy of the universe). The entropy of a system may decrease, but the entropy of the system plus its surroundings must always increase.Highly ordered living organisms do not violate the second law because they are open systems. For example, animals: Maintain highly ordered structure at the expense of increased entropy of their surroundings. Take in complex high energy molecules as food and extract chemical energy to increase and maintain order. Return to the surroundings simpler low energy molecules (CO2 and water) and heat.Energy can be transformed, but part of it is dissipated as heat which is largely unavailable to do work. Heat energy can perform work if there is a heat gradient result in heat flow from warmer to cooler.
Combining the first and second laws; the quantity of energy in the universe is constant, but its quality is not.
Entropy = Quantitative measure of disorder that is proportional to randomness...
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